 LIB "purityfiltration.lib";
ring D = 0,(x,y,z),dp;
matrix R[7][3]=
0 ,0,1,
1 ,4*x+z,z,
1,8*x2*z,z,
1 ,0 ,0,
0 ,xy,0,
0 ,xy,y,
0 ,0 ,x;
// coker(R) is 2pure, so all doubleExt are zero
print(doubleExt(transpose(R),0));
==> 1
print(doubleExt(transpose(R),1));
==> 1,0,0,
==> 0,1,0,
==> 0,0,1
print(doubleExt(transpose(R),3));
==> 1
// except of the second
print(doubleExt(transpose(R),2));
==> 4yz,4xz
